Venezuela's National Guard fired tear gas on residents clearing a barricaded border bridge to Colombia on Saturday, as the opposition began making good on its high-risk plan to deliver humanitarian aid despite objections from President Nicolas Maduro.
By midday, opposition leader Juan Guaido pulled himself on to a truck and shook hands with its driver as he and Colombian President Ivan Duque gave a ceremonial send off to an aid convoy.
The convoy wants to transport nearly 200 metric tons of mostly US-supplied emergency food and medical supplies from the Colombian city of Cucuta.
'Our call to the armed forces couldn't be clearer: put yourself on the right side of history,' said Guaido, in an appeal to troops who constitute Maduro's last-remaining major plank of support in a country ravaged by hyperinflation and widespread shortages.
The opposition is calling on masses of Venezuelans to form a 'humanitarian avalanche' to escort trucks carrying the aid across several border bridges.
A line of heavy trucks packed with aid supplies waited to attempt the crossing, in front of rows of television cameras.
U.S. President Donald Trump's national security adviser John Bolton cancelled plans to travel to South Korea to prepare for a summit addressing North Korea's nuclear program in order to focus instead on events unfolding in Venezuela, his spokesman said on Friday.
'To Maduro's military cronies attacking civilians at the Brazilian border - the world is watching and the perpetrators will face justice,' Bolton wrote on Twitter. 'The Venezuelan military should protect civilians, not shoot them.
Guaido, 35, head of the opposition-run Congress, has provided few details on the transport plan. Trucks are expected to be driven by Venezuelan volunteers and some opposition figures have suggested forming human chains.
Maduro blames the country's dire situation on U.S. sanctions that have blocked the country from obtaining financing and have hobbled the OPEC nation's oil industry.
Concerns about the potential for violence flared on Friday when the Venezuelan army opened fire in a village near the Brazilian border after indigenous leaders attempted to prevent them from advancing, killing a woman and her husband.
The U.S. government condemned the killings.
The U.S. envoy for Venezuela, Elliott Abrams, who travelled to Cucuta on Friday, called them 'a crime and a disgrace', while the U.S. State Department said 'egregious violation of human rights by Maduro and those who are following his orders will not go unpunished.'
Venezuelan troops on Saturday morning had blocked the Brazilian border despite protests by villagers in the nearby town of Santa Elena de Uairen who burned a bus, a truck and a National Guard office overnight.
'The situation is critical and we should be all united to allow the aid to pass,' said shopkeeper Jeremy Ortega, 21.
Brazil sent two small trucks with food and medicine to the border on Saturday, after the border closure foiled its plan to have more Venezuelans drive vehicles to pick up the 200 tonnes of aid it has stockpiled in the northern city of Boa Vista.
Brazilian Foreign Minister Ernesto Araujo urged Venezuela's military to let the trucks in.
Nearly 200,000 people attended a benefit concert in Cucuta on Friday featuring Latin pop stars, including Luis Fonsi of 'Despacito' fame, many of whom called on Maduro to step down.
A rival concert held by the ruling Socialist Party on the Venezuelan side was sparsely attended.
Guaido in January invoked articles of the constitution to assume interim presidency and denounced Maduro as a usurper, arguing his 2018 re-election was illegitimate.